Multi-channel switching system



Jan. 3, 1967 D. E. QUINLAN 3,296,499

MULTI CHANNEL SWITCHING SYSTEM Filed Aug. 5, 1963 POWER gM/m/P-vvvvw/T SUPPLY l l De* INVENTOR. I TLN CN 'LF/DONALD E. QUIN LAN l ATTORNEY United States Patent ilice n 3,296,499 Patented Jan. 3, 1967 3,296,499 MULTI-CHANNEL SWETCHHNG SYSTEM Donald E. Quinlan, Lincoln Park, N 1., assigner to Visual Electronics Corporation, a corporation of New York Filed Aug. 5, 1963, Ser. No., 300,023 7 Claims. (Cl. 317-154) This invention relates to electrical switching systems, and more particularly to an electromagnetic relay controlled, multi-channel switching system, which utilizes a common holding circuit to allow momentary push button, On and Olf control of each channel.

It is often desirable to provide a multi-channel switching system wherein an operator is able to push a button and switch On a desired channel, while at the same time the previously On channel is switched Off. One particular application for a push button controlled switching system is in radio or television broadcasting wherein it is necessary to provide a system to permit an operator to select one from a number of video or audio sources for programming. The control system for such a multi-channel switching system normally comprises a row of momentary On push buttons, one for each selected source,

A common prior art arrangement for achieving this function is to bring the audio or Video signals directly to an organization of mechanically locked push button switches having multiple contacts for each switch. A mechanical locking bar arrangement is usually provided so that by pressing any push button one of the previously locked buttons will 'be released to achieve the desired switching operation. This arrangement -requires that the audio and video signals be fed directly into the switching console. It has the disadvantage of requiring specially shielded lines of considerable length and specially constructed mechanical switching equipment. Therefore, a relay switching arrangement is often used, with the relays for performing the actual switching being located in a remote location preferably near the equipment to be switched, whereas the control buttons are located on a central console near the operator. Although it is possible with a relay system to use mechanically locked push buttons with a locking bar arrangement, it is yet more convenient to use electrically locked relays.

A prior art arrangement often used to provide electrical lock up, utilizes a plurality of individual relays for each circuit to be switched, and also includes a holding relay with a holding circuit common to selected holding contacts of each individual channel relay. Circuitry is provided so that momentary On push buttons may be used which close circuits to each channel relay and also to the common holding relay, which operates to break the previously energized relay holding circuit. When the momentary On push button is released, the holding relay quickly re-establishes a holding circuit for the newly selected relay through its holding contacts and thus places its associated channel into operation. This arrangement has the disadvantage that the holding relay must operate very quickly and establish a new holding circuit before the contacts of the newly operated relay open. This requires that the holding relay have a very fast release time, at least faster than all of the channel relays, so that the new holding circuit is established before the holding contacts of the selected channel open. Such a relay is quite expensive and somewhat more expensive than the individual channel relays. Also, the relay is subject to greater wear than the channel relays as it must operate each time a new channel is selected, whereas the channel relays are operated only when their respective channels are selected. Furthermore, such a circuit with a common holding relay requires a number of circuit directing diodes for each relay if the control wiring is to be kept at a minimum.

It is therefore an object of the present invention to provide a multi-channel switching system which eliminates the common, electro-mechanical holding relay.

It is another object of the invention to provide a multichannel switching circuit which eliminates control current directing diodes and minimizes the necessary interconnecting circuit wiring.

It is a further object of the invention to provide a multi-channel switching system which utilizes a minimum number of component parts.

It is still another object of the invention to provide a multi-channel switching system which utilizes solid state components to perform holding circuit functions occur'- ring for each switching operation.

The features of this invention, which are believed to be novel, are set forth with particularity in the appended claim-s. The invention, together with further objects. and advantages thereof, may be best understood, however, by reference to the following description taken in conjunction with the accompanying drawing. The drawing merely shows, and the description merely describes, a preferred embodiment of the present invention which is given by way of illustration or example.

Referring now to the drawing, a relay switching circuit for three channels and an Nth channel are shown since as many channels as desired may be switched. Each channel has a momentary On push button PB1-PBN comprising a pair of normally open contacts preferably mounted on a suitable control console at a convenient location for the operator. Connected to each xed contact of PBl-PBN is a tally lamp TLl-TLN which lights when its associated push -button is operated, but stays lit while the associated channel is in use.

Each xed contact of push button PBI-PEN is connected to a respective channel relay Kl-KN which has holding contacts Kla-KNa and utilization7 contacts K1b-KNb- While each relay may have as many sets of utilization contacts as may be desired, for the sake of simplicity only one set is shown. These contacts may be used to switch any selected circuits, for example, audio or video signal lines.

The fixed contacts of contacts K1a-KNa are connected to the same terminal of their respective actuating coils of relays Kl-KN as each of the xed contacts of push buttons PBrl-PBN. The movable contacts of contacts Kla-KNa are serially connected to each other and to line 10. The other terminals of the actuating coils of relays Kl-KN are each connected to ground. Across the terminals of these coils are connected capacitors Ol-CN.

Line 10 is connected to a switching amplifier, which, for purposes of illustration is shown as a transistor, although other suitable switching anrplifers may be used. More particularly, the line is connected to the collector electrode of a transistor Q1. A capacitor 13 is connected between this electrode and ground, and serves to suppress transient switching voltages. The emitter electrode of the transistor is connected to line 12 to which also is connected all of the movable contacts of push buttons PB1-PBN- A voltagedivider comprising serially connected resistors 14, 16 and 18 is connected between the emitter electrode of transistor Q1 and ground. The base electrode is connected to the junction point of resistors 16 and 18. The junction point of resistors d4 and 16 is connected to a suitable source of D.C. potential 20 which, for example, may be minus 28 volts.

The operation of the multi-channel switching system will now be described. Assume that relay K1 is energized and that contacts Kla and Klb are closed. Holding current for relay K1 is obtained from .power supply 20 through resistor 114, transistor Q1, line 10, and closed contacts Kla.

' resistor 18 may be 2 kilohms.

' tacts K3a and K3b to close.

Transistor Q1, which is an NPN transistor, is in a conducting state because of the voltage divider action of resistors 14, 16 and 18. Resistor 14 may, for example, be Va 47 ohm resistor, resistor 16 may be l0() ohms, and Due to the presence of resistor 14 in the circuit, the emitter of transistor of Q1 -is at a lower potential than the minus 28 volts applied to the junction of resistors 14 and 16, and the base is at an even more positive potential than the emitter due to the potential appearing at the junction point of resistors 116 and 1S. Under these conditions, transistor Q1 will conduct current from its collector to its emitter and maintain relay K1 in an energized condition. Tally lamp TL1 also remains lighted as it is connected across the terminals of the actuating coil of relay K1.

Assume now that the push button for any of the other channels, for example, CH3, is pushed momentarily. Pressing of push button yPBS will apply voltage to the actuating coil of relay K3 through line 12 and cause con- F or a short interval of time both relays K1 and K3 are energized. This will cause substantially twice as much current as formerly to flow through resistor 14. The voltage drop across resistor 14 doubles accordingly, so that the emitter of transistor Q1 becomes positive with respect to its base and the transistor is cut off. This action causes relay K1 to become de-energized and allow holding contacts Kla to open. Due to the value of capacitor C1 which may be 1A() mfd., the same as capacitors CIZ-CN, this de-energizing action occurs smoothly and insures that relay K3 is energized before contacts Kla and Klb are opened. Thus, if audio or video program material is being switched, a break in the program continuity will not occur.

As soon as relay K1 releases, the drop across resistor 14 returns to normal, transistor Q1 conducts again and a holding path is immediately re-established through holding contacts K3a. Relay K3 remains locked .up and tally lamp K3 lights and remains lit when the operator removes his nger from button PBS.

A holding circuit for a plurality of relays is therefore provided :by the present invention, which eliminates the need for a sensitive electromechanical relay and utilizes all solid state components.

It will be noted that in accordance with the present invention, the tally lamps TLl-TLN are able to be connected directly to the push button switch contacts and thus mounted at the most convenient and logical location without the need for additional wiring to separate relay contacts in order to cause the lamp to stay lit while its associated channel is in active use.

While the switching amplifier is shown by way of eX- ample as being an NPN transistor, it will be understood that the invention will function equally as well with a PNP transistor by merely changing the polarity of voltage from supply 20.

The invention hereinabove described lmay therefore be varied in construction with the scope of the claims, for the particular device selected to illustrate the invention is but one of many possible embodiments of the same. The invention, therefore, is not to be restricted to the precise details of the structure shown and described.

I claim:

1. In a multi-channel switching system having a plurality of channel switching relays, each of said relays having at least a pair of normally open contacts, a holding circuit for said relays comprising, a source of potential having a common output terminal, a bias potential terminal, and an energizing potential terminal, said source of potential having means for developing a selected bias potential between said bias terminal and said common output terminal and a selected energizing potential between said energizing potential terminal and said cornmon output terminal, an impedance connected to said common output terminal, individual switch means each serially connected to salid impedance to form a common junction point and to an associated relay for selective actuation thereof, a switching amplifier having conducting and non-conducting states and pairs of input and outp-ut terminals, said pairs of input terminals being connected to said bias terminal and to said common junction point, said bias potential being effective to bias said switching amplifier into a conducting state, said relays having a common terminal connected to said energizing potential terminal, one of said amplifier output terminals being connected to said common junction point, and circuit means including said pairs of normally open contacts for connecting the other of said switching ampliiier output terminals to the junction point of a selected switch and its associated relay whenever 4the associated relay is energized and said normally open contacts are closed, thereby for-ming a first individual holding circuit for the associated relay through the conducting switching amplifier and the associated, now closed, normally open contacts, said switching amplifier being rendered non-conductive by the increase in potential developed across said impedance to open said first holding circuit, whenever a second selected switch is closed, said amplifier remaining non-conductive until a second individual holding circuit for said second selected switch is formed by said circuit means.

2. The invention defined in claim 1 wherein said circuit means includes means associated with each of said relays and actuated thereby for preventing simultaneous energization of a plurality of said individual holding circuits.

3. The invention defined in claim 2 wherein said means for preventing simultaneous energization of a plurality of said individual holding circuits includes interconnected, interlocking contacts associated with each of said relays.

4. The invention defined in claim 1 wherein said switching ampliiier includes a transistor having base, emitter and collector electrodes, said emitter and collector electrodes being connected respectively to the common junction point between said impedance and said switches and to the other of said switching amplifier output terminals, said base electrode being connected to said bias potential terminal, said increase in potential developed across said y impedance whenever one of said switch means is actuated being suicient to bias said transistor into a non-conducting state and de-energize said first energized velay.

5. The invention detined in claim 1 including delay means associated with each relay for causing said first selected relay to become slowly deenergized after said second relay becomes energized.

6. The invention defined in claim 5 wherein each of said relays has an actuating coil and said delay means includes a capacitor connected across the -terminals of each of said actuating coils, said capacitor lbeing effective to discharge through said coil and maintain said first relay in an energized condition for a predetermined period of time after said switching amplifier ceases to conduct.

7. The invention defined in claim 4 wherein the value of said impedance is sufiicient to allow said transistor to conduct and hold one of said relays in an energized condition when the contacts associated `therewith have been closed, the momentary closing of one of said s/Witch means being effective to energize an associated relay and cause the potential across said impedance to increase to a magnitude suthcient to bias said transistor to cut off and de-enerfgize any previously held relay.

References Cited by the Examiner UNITED STATES PATENTS 2,971,135 2/1961 Ebert 317-154 X 3,181,068 4/1965 Feldhake 317-137 X 3,184,734 5/1965 Uren et al. v317140 X MILTON O. HIRSHFIELD, Primary Examiner.

SAMUEL BERNSTEIN, Examiner.

L. T. H'lX, Assistant Examiner. 

1. IN A MULTI-CHANNEL SWITCHING SYSTEM HAVING A PLURALITY OF CHANNEL SWITCHING RELAYS, EACH OF SAID RELAYS HAVING AT LEAST A PAIR OF NORMALLY OPEN CONTACTS, A HOLDING CIRCUIT FOR SAID RELAYS COMPRISING, A SOURCE OF POTENTIAL HAVING A COMMON OUTPUT TERMINAL, A BIAS POTENTIAL TERMINAL, AND AN ENERGIZING POTENTIAL TERMINAL, SAID SOURCE OF POTENTIAL HAVING MEANS FOR DEVELOPING A SELECTED BIAS POTENTIAL BETWEEN SAID BIAS TERMINAL AND SAID COMMON OUTPUT TERMINAL AND A SELECTED ENERGIZING POTENTIAL BETWEEN SAID ENERGIZING POTENTIAL TERMINAL AND SAID COMMON OUTPUT TERMINAL, AN IMPEDANCE CONNECTED TO SAID COMMON OUTPUT TERMINAL, INDIVIDUAL SWITCH MEANS EACH SERIALLY CONNECTED TO SAID IMPEDANCE TO FORM A COMMON JUNCTION POINT AND TO AN ASSOCIATED RELAY FOR SELECTIVE ACTUATION THEREOF, A SWITCHING AMPLIFIER HAVING CONDUCTING AND NON-CONDUCTING STATES AND PAIRS OF INPUT AND OUTPUT TERMINALS, SAID PAIRS OF INPUT TERMINALS BEING CONNECTED TO SAID BIAS TERMINAL AND TO SAID COMMON JUNCTION POINT, SAID BIAS POTENTIAL BEING EFFECTIVE TO BIAS SAID SWITCHING AMPLIFIER INTO A CONDUCTING STATE, SAID RELAYS HAVING A COMMON TERMINAL CONNECTED TO SAID ENERGIZING POTENTIAL TERMINAL, ONE OF SAID AMPLIFIER OUTPUT TERMINALS BEING CONNECTED TO SAID COMMON JUNCTION POINT, AND CIRCUIT MEANS INCLUDING SAID PAIRS OF NORMALLY OPEN CONTACTS FOR CONNECTING THE OTHER OF SAID SWITCHING AMPLIFIER OUTPUT TERMINALS TO THE JUNCTION POINT OF A SELECTED SWITCH AND ITS ASSOCIATED RELAY WHENEVER THE ASSOCIATED RELAY IS ENERGIZED AND SAID NORMALLY OPEN CONTACTS ARE CLOSED, THEREBY FORMING A FIRST INDIVIDUAL HOLDING CIRCUIT FOR THE ASSOCIATED RELAY THROUGH THE CONDUCTING SWITCHING AMPLIFIER AND THE ASSOCIATED, NOW CLOSED, NORMALLY OPEN CONTACTS, SAID SWITCHING AMPLIFIER BEING RENDERED NON-CONDUCTIVE BY THE INCREASE IN POTENTIAL DEVELOPED ACROSS SAID IMPEDANCE TO OPEN SAID FIRST HOLDING CIRCUIT, WHENEVER A SECOND SELECTED SWITCH IS CLOSED, SAID AMPLIFIER REMAINING NON-CONDUCTIVE UNTIL A SECOND INDIVIDUAL HOLDING CIRCUIT FOR SAID SECOND SELECTED SWITCH IS FORMED BY SAID CIRCUIT MEANS. 